Capillary electrophoresis is a well known form of high performance electrophoresis (HPE) and a highly effective means of analyzing extremely small biological samples. The long separation path in a capillary permits the separation of a multitude of components in a single sample, including components which are closely related. The thin diameter of a capillary permits the use of a high voltage, which produces separations in a relatively short period of time. Furthermore, capillaries are particularly well suited for on-line detection of the separated species using a light beam passing through the capillary directly into a detector.
Capillary electrophoresis has been facilitated considerably by the use of cartridges to contain the capillaries. Cartridges eliminate the need for the operator to handle the capillary directly, and permit easy and secure connections with associated devices and apparatus such as electrode chambers, sample reservoirs and detection apparatus. Cartridges also offer means of cooling of the capillary. This is done in some cartridges by the contact of the capillary with heat-dissipating materials of extended surface areas, and in others by contact with a coolant circulating through the cartridge.
The ability of a cartridge to be easily and rapidly connected with and disconnected from its associated components is generally achieved at the cost of smooth and efficient fluid flow in and out of the cartridge. Since the capillary ends must be protected from breakage, the small internal diameter of the capillary is not continued through most fittings, and the result is dead space in the fitting. Dead space interferes with the loading of sample into the capillary as well as the elution and clearance of separated sample components from the capillary. Other problems include the cooling efficiency, notably the uniformity and continuity of coolant flow along the entire capillary length. Dead space in the coolant flow path and unequal coolant rates along the capillary length affect the response of the capillary to the coolant and the reliability and reproducibility of the results.